JPH0610673A - Direct injection type diesel engine - Google Patents

Abstract

PURPOSE:To reduce NOx while suppressing generation of the smoke in the whole load range of an engine by partitioning off two combustion chambers with a recessed part on the crown of a piston and an intermediate wall, and taking the countermeasures of communication by a slit or the like, thereby improving the pilot injection. CONSTITUTION:The pilot injection is executed in advance of the main injection in this direct injection type diesel engine. In this case, a first and a second combustion chambers 8, 9 are partitioned off by a recessed part 1b formed inside of an outer circumferential wall 1a on the crown of a piston 1 and an intermediate wall 1c which is vertically provided on the recessed part 1b. The respective combustion chambers 8, 9 are connected to each other by a slit 1d. The main injection is constituted so as to pass the slit 1d. The pilot injection is constituted so as to be collided against the intermediate wall 1c. In addition, both the pilot injection and the main injection are executed except in the high load condition of the engine, while only the main injection is executed in the high load condition. This arrangement improves the pilot injection, and reduces generation of the smoke and NOx.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a direct injection diesel engine in order to significantly reduce the NO _X (nitrogen oxides) while maintaining the generation of smoke at a low level.

[0002]

2. Description of the Related Art At present, reduction of smoke and NO _x is an important issue in diesel engines, and in order to reduce them, high pressure injection, improvement of combustion system, exhaust gas recirculation (EG
Various proposals such as R) have been made. Of these, EGR
Have problems of durability and reliability such as deterioration of fuel consumption and smoke, corrosion of EGR device due to exhaust gas or deterioration of function.

From the viewpoint of the combustion system, in the case of low pressure injection which is widely used at present, after the spray is ignited in the vicinity of the nozzle, it progresses while being wrapped in the whole flame. At this time, the spray is air. At the same time, it burns while energizing the burnt gas generated by itself, so a high temperature part and an oxygen deficient part are formed in the center of the spray, which becomes a cause of smoke
It is said that entrainment of burnt gas acts as a negative factor. Therefore, in order to reduce smoke, it is necessary to mix fuel and air quickly, and methods such as swirl and squish are used to improve the air utilization rate. Since the mixing speed also increases, there is a contradictory problem that the heat generation rate in the early stage of combustion increases due to the increase in premixed combustion, leading to an increase in NO _X , which makes it difficult to reduce smoke and NO _X simultaneously. ing.

In order to solve the above problems, there is known a system in which a high pressure injection (for example, an injection pressure of 1000 kg / cm ² or more), a small injection hole nozzle, a shallow dish combustion chamber and a low swirl are combined. Referring to FIG. 9, 1 is a piston, 2 is a piston ring, 3 is a cylinder liner, 4 is a gasket, 5 is a cylinder head, and 6 is a fuel injection valve having a nozzle 7. A chamber 9 is formed. When the piston 1 rises and reaches the vicinity of the top dead center, the spray F of the fuel injected from the nozzle 7 ignites at once in the vicinity of the wall surface 10, and then the flame H expands toward the center of the combustion chamber 9, The center remains as a non-combustible area until the end of injection. That is, the spray progresses while sufficiently entraining air on the side of the non-combustible region near the center of the combustion chamber 9 until it reaches the wall surface 10, and on the side of the wall surface 10 there is a two-stage combustion path that collides with the wall surface 10 while introducing burned gas Follow In the case of high-pressure injection, even if the injection timing is significantly delayed, ignition will occur. Therefore, in combination with the injection timing delay, it is possible to reduce smoke and NO _X simultaneously as compared with low-pressure injection.

[0005]

However [0007], As you significantly delayed injection timing, the ignition delay increased, as shown in FIG. 10, NO _X is increased by NO _X be delayed any further injection timing again It cannot be reduced. To improve this,
Pilot injection is under consideration to shorten ignition delay and ensure ignition. FIG. 11 shows an example in which the pilot injection can significantly delay the injection timing and greatly reduce the NO _X, but since the injection is performed at 20 to 30 ° after TDC, the fuel efficiency is significantly deteriorated.

Further, in the case of high-pressure injection, as shown in FIG. 12, NO _X tends to be high in the medium load region, and in order to solve this, air introduction is suppressed in the medium load region and entrainment of burned gas is involved. If you can increase the
The generation of _X can be suppressed.

To further describe the pilot injection, in the case of low pressure injection, when the pilot injection is performed, the combustion flame of the pilot spray spreads from the center of the combustion chamber 9 to the wall surface 10 as shown in FIG. 13A. Proceed through the flame while introducing burnt gas (internal EGR)
As a result, NO _x will fall, but smoke will deteriorate significantly. On the other hand, in the case of high-pressure injection, since the energy of the spray is large, as shown in FIG. 13B, the pilot flame also ignites and burns in the vicinity of the wall surface 10 of the combustion chamber, so the main spray introduces burned gas from the pilot flame. There is no. Further, since the high-pressure injection reduces NO _X , when the injection timing is significantly delayed, the pilot spray goes out of the combustion chamber 9 as the piston 1 descends, as shown in FIG. 13C. Therefore,
When pilot injection is performed with high-pressure injection, it is difficult to simultaneously satisfy the above-mentioned problems of delaying the injection timing and suppressing the introduction of air in the medium load range to increase the entrainment of burnt gas to reduce NO _X at the same time. Is.

In the case of high pressure injection, the energy of the spray is large and ignition occurs on the wall surface of the combustion chamber. Therefore, unlike the low pressure injection, the spray is not entrained in the burnt gas during the injection period, and the vicinity of the nozzle is There is always an air layer.
Therefore, if it is possible to control so that the burnt gas is positively introduced into the spray in the medium load range, NO _X can be reduced under a partial load without smoke generation, and highly efficient internal EGR can be achieved. The idea that this can be done has been proposed before (motor fan, May 1992, p. 54). However, no practical structure or research announcement has been made so far regarding the specific structure for introducing burnt gas into the spray.

The present invention solves the above problems by improving the conventional pilot injection to maintain the smoke generation at a low level over the entire load range of the engine while maintaining the N level.
And to provide a direct injection diesel engine of O _X can be greatly reduced.

[0010]

Therefore, the direct injection diesel engine of the present invention is a direct injection diesel engine that enables pilot injection prior to main injection.
A first partition defined by a hollow portion 1b formed at the top of the piston 1 and an intermediate wall 1c provided upright in the hollow portion 1b.
The combustion chamber 8 and the second combustion chamber 9, and the first combustion chamber 8 and the second combustion chamber
A slit 1d communicating with the combustion chamber 9, the main injection is configured to pass through the slit 1d, the pilot injection is configured to collide with the intermediate wall 1c,
It is characterized in that pilot injection and main injection are performed except when the engine load is high, and only main injection is performed when the engine load is high. It should be noted that the numbers added to the above configurations are for comparison with the drawings for easy understanding, and the configurations of the present invention are not limited thereby.

[0011]

In the present invention, for example, as shown in FIG.
When the engine load is low except for a high load, the pilot-injected spray collides with the intermediate wall 1c of the first combustion chamber 8 and ignites, and then the main spray is injected and the burned gas in the first combustion chamber 8 is injected. While passing through the slits 1d of the first combustion chamber 8 to enter the second combustion chamber 9 and burn. Therefore, the generation of NO _X at the partial load is suppressed. On the other hand, in the high load region, the pilot injection is stopped and only the main spray is supplied, whereby the main spray introduces the air in the first combustion chamber 8 while
Since the air in the second combustion chamber 9 is introduced through the slit 1d and collides with the outer peripheral wall 1a to ignite and burn, it is possible to suppress the deterioration of smoke.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a direct injection diesel engine 1 according to the present invention.
FIG. 3 is a plan view and FIG. 3B is a sectional view taken along the line BB of FIG.

Reference numeral 1 is a piston, 2 is a piston ring, 3 is a cylinder liner, 4 is a gasket, 5 is a cylinder head, and 6 is a fuel injection valve having a nozzle 7.
Has six injection holes to inject fuel,
The number of injection holes is not limited. The piston 1 has an outer peripheral wall 1a formed at the top, a recessed portion 1b formed inside thereof, an intermediate wall 1c standing on the recessed portion 1b, and a slit formed at a predetermined interval in the intermediate wall 1c. 1d, and the first combustion chamber 8 and the second combustion chamber 9 are formed by the intermediate wall 1c. Then, the pilot spray injected from the nozzle 7 collides with the intermediate wall 1c, and the main spray passes through the slit 1d and collides with the outer peripheral wall 1a.

In the present invention, since the injection positions of the pilot injection and the main injection are different, a general injection valve cannot be used. Therefore, the fuel injection valve 6 uses a conventionally known valve that can change the injection position. For example, the device shown in Japanese Utility Model Publication No. 63-27093 will be described with reference to FIG. FIG. 2A is a sectional view of a fuel injection valve,
2B is a plan view seen from the direction B in FIG. 2A.

The fuel injection valve 6 has a first needle valve 13 fitted in the outer cylinder 12 and a second needle valve 13 fitted in the first needle valve 13.
Of the needle valve 14, the first set of injection holes 15, 15 formed in the nozzle 7 of the outer cylinder 12, and the second set of injection holes 16, 16, formed in the tip thereof. And a first fuel supply passage 17 and a second fuel supply passage 18 formed in the outer cylinder 12.
And the first and second needle valves 13 and 14 are urged downward in the drawing by springs (not shown). The first fuel supply passage 17 includes the outer cylinder 12 and the first needle valve 1.
3 through the passage 19 formed between the first injection hole 1
The second fuel supply passage 18 is made to be able to communicate with 5, 15 ,.
Through the passages 20 and 21 formed between the first needle valve 13 and the second needle valve 14, the second set of injection holes 16, 16 ,.
It is possible to communicate with.

The main spray injected from the first set of injection holes 15, 15, ... Is made to collide with the outer peripheral wall 1a through the slit 1d of FIG. 1A, and the second set of injection holes 16 is formed. ,
The pilot sprays injected from 16, ... Are arranged so as to collide with the intermediate wall 1c of FIG. 1A.

FIG. 3 is a block diagram of the fuel supply system, and FIG.
The first and second fuel supply passages 17 and 18 are connected to a common rail 24 and a high-pressure pump 25 via a main injection control solenoid valve 22 and a pilot injection control solenoid valve 23, respectively, and these are connected to an electronic control unit. At 26, it is controlled by signals from the engine speed sensor 27 and the engine load sensor 28.

4 and 5 show another embodiment of the direct injection type diesel engine of the present invention, FIG. 4A is a plan view, and FIG.
4B is a sectional view taken along the line BB of FIG.
FIG. 5 is a configuration diagram of the fuel supply system. The same components as those in the above-described embodiment are designated by the same reference numerals and the description thereof will be omitted.

In this embodiment, two valves, a main injection valve 6a and a pilot injection valve 6b, are used, and the injection hole of the nozzle 7a of the main injection valve 6a passes through the slit 1d and the outer peripheral wall 1a.
To the nozzle 7 of the pilot injection valve 6b.
The nozzle hole of b is arranged so as to collide with the intermediate wall 1c. In this case, one pump 25 may be used to supply the main injection valve 6a and the pilot injection valve 6b as shown in FIG. 5, or separate pumps may be used.

Next, the control method of the direct injection type diesel engine of the present invention will be described. 6 is a block diagram of the control system,
FIG. 7 is a diagram showing control data, and FIG. 8 is a diagram showing a control flow.

The detection signals of the engine speed sensor 27 and the engine load sensor 28 are input to the electronic control unit 26, where they are compared, calculated and processed based on the control data stored in the memory 29, and their output signals are output. Is a main injection control solenoid valve 22 and a pilot injection control solenoid valve 2
3 is output. The memory 29 stores the control data shown in FIG. 7, and the processing shown in FIG. 8 is performed. That is, the current engine load L is equal to the predetermined engine load L ₁
If it is larger than the load L ₁ , the main injection is performed after the pilot injection, and the main injection is performed when the load L ₁ is exceeded, and the main injection is performed only when the load L ₁ is exceeded. The solenoid valve 23 is controlled.

Therefore, when the engine load is low except for a high load, the spray injected as a pilot collides with the intermediate wall 1c of the first combustion chamber 8 and ignites, and then the main spray is injected as the first spray.
While entraining the burned gas in the combustion chamber 8, it enters the second combustion chamber 9 through the slit 1d of the first combustion chamber 8 and burns. Therefore, the generation of NO _X at the partial load is suppressed. As described with reference to FIG. 12, the smoke concentration originally has a sufficient margin in the low load region and the medium load region, and the adverse effect on the smoke due to the introduction of the burnt gas is small. On the other hand, in the high load region, the pilot injection is stopped and only the main spray is supplied, whereby the main spray passes through the slit 1d of the first combustion chamber 8 and introduces the air in the first combustion chamber 8 into the second combustion chamber 9. Outer wall 1a
Smoke can be prevented from being deteriorated because it collides with and is ignited and burned. Incidentally, originally NO _X concentration as in the high load region described in FIG. 12 is low.

[0023]

As is apparent from the above description, according to the present invention, in a direct injection diesel engine that enables pilot injection prior to main injection, a recess formed at the top of the piston and the recess. A first combustion chamber and a second combustion chamber that are partitioned by an intermediate wall that is erected on the first combustion chamber, and a slit that connects the first combustion chamber and the second combustion chamber,
The main injection is configured to pass through a slit, the pilot injection is configured to collide with the intermediate wall,
Since pilot injection and main injection are performed except when the engine is under high load, and only main injection is performed when the engine is under high load,
While improving the conventional pilot injection and keeping the generation of smoke at a low level over the entire engine load range, NO _X
Can be significantly reduced.

[Brief description of drawings]

1 shows an embodiment of a direct injection type diesel engine of the present invention, FIG. A is a plan view, and FIG. B is a sectional view taken along the line BB of FIG.

2 shows a fuel injection valve used in the embodiment of FIG.
FIG. A is a sectional view, and FIG. B is a plan view seen from the direction B of FIG.

FIG. 3 is a configuration diagram of a fuel supply system in the embodiment of FIG.

FIG. 4 shows another embodiment of the direct injection type diesel engine of the present invention, FIG. A is a plan view, and FIG. B is a sectional view taken along the line BB of FIG.

5 is a configuration diagram of a fuel supply system in the embodiment of FIG.

FIG. 6 is a configuration diagram of a control system according to the present invention.

FIG. 7 is a diagram showing control data in the present invention.

FIG. 8 is a diagram showing a control flow in the present invention.

FIG. 9 shows an example of a conventional direct injection diesel engine,
Figure A is a sectional view and Figure B is a plan view

FIG. 10 is a diagram for explaining the relationship between fuel injection timing, ignition delay time, NO _X concentration, and smoke concentration.

FIG. 11 is a diagram for explaining the relationship between fuel injection timing and NO _X concentration depending on the presence or absence of pilot injection.

FIG. 12 is a diagram for explaining the relationship between engine load and NO _X concentration and smoke concentration.

FIG. 13 is a diagram for explaining pilot injection for explaining the problems of the present invention.

[Explanation of symbols]

1 ... Piston, 3 ... Cylinder, 5 ... Cylinder head, 6
... fuel injection valve 7 ... nozzle, 8 ... first combustion chamber, 9 ... second combustion chamber, 1a ...
Outer peripheral wall, 1b ... Recessed portion 1c ... Intermediate wall, 1d ... Slit

Front page continuation (72) Inventor Kinji Tsujimura 2530, Kuma, Tsukuba-shi, Ibaraki Japan Automobile Research Institute Co., Ltd. Shin Combustion System Research Co., Ltd.

Claims (1)

[Claims] 1. A direct injection diesel engine that enables pilot injection prior to main injection, and a first section defined by a recess formed at the top of the piston and an intermediate wall standing upright in the recess. A combustion chamber and a second combustion chamber,
It has a slit that connects the first combustion chamber and the second combustion chamber, the main injection is configured to pass through the slit, the pilot injection is configured to collide with the intermediate wall, A direct-injection diesel engine characterized by performing pilot injection and main injection except during load, and performing only main injection during high engine load.